1. Field of the Invention
The present invention relates to a rolling bearing to be suitably used for high speed rotation as superchargers or metal machine tools.
2. Description of the Related Art
Since the rolling bearing is repeatedly effected with shearing stress at race surfaces and rolling surfaces under high surface pressure, even in case of no especial abnormal conditions, pitching or flaking occur some day due to rolling fatigue, and its life ceases before long. For lengthening the rolling fatigue life, high carbon Cr bearing steel as SUJ2 has conventionally been used as a material for forming the bearing member. Otherwise, developments of steel materials enabling to lengthen the rolling fatigue life have energetically been made (see JP-A-5-25609, hereinafter, xe2x80x9cJP-Axe2x80x9d means xe2x80x9cUnexamined Japanese Patent Publication (kokai)xe2x80x9d).
However, when the rolling bearing is served under the high rotation as dmn value (the product of an average size dm of an inner diameter and an outer diameter of the bearing ≈ the diameter Dp (mm) of the pitch circle of the rolling element and the rotation number n (rpm)) being 1.0xc3x97106 or more, since PV value designating friction conditions (P: surface pressure and V: velocity) is high, the sliding friction caused between the rolling element and the raceway surface, such problems as friction or seizing occur before going to the rolling fatigue life. This is because, for example, in a ball bearing, the friction is large by the spin sliding, and in a roller bearing, the friction between the roller and flanges of the inner and outer races is large. In particular, when seizing occurs in the bearing, as troubles of a machine itself furnishing with this bearing are possibly induced, prevention of seizing is very important.
For solving such problems, it has been proposed to form the inner and outer races and the rolling element with heat resistant alloy steels as M50 or the like. However, in this method, abrasion resistance is improved, but seizing resistance is hardly effective. Accordingly, there have been proposed a method of improving the seizing resistance by forming films of desired materials on the raceway surfaces and the surfaces of the rolling elements fabricated with the heat resistant alloy steel as M50, or a method of forming the inner and outer races with ceramics. Further, it has been proposed to heighten the seizing resistant property by improving a lubricating method.
However, among the conventional techniques, the methods of forming the films or employing the ceramics as the materials forming the bearing members bring about high material cost and reduce productivity, resulting in high production cost. Further, the improvement of the lubricating method cannot be often used depending upon machines equipped with the bearings.
It is an object of the present invention to provide a rolling bearing enabling to prevent abrasion or seizing even when these are served even under the high speed rotation of the dmn value being 1.0xc3x97106 or more, and are low of the production cost.
In the present invention, a rolling bearing comprises an inner race, an outer race and a plural rolling elements. At least one of the inner race, the outer face and the rolling elements comprises a steel element containing: 0.2 to 1.2 wt % of C; 0.7 to 1.5 wt % of Si; 0.5 to 1.5 wt % of Mo; 0.5 to 2.0 wt % of Cr; and 12 ppm or less of O. The at least one of the inner race, the outer race and the rolling elements is carbonitrided and thereafter quenched and tempered so that carbon concentration on a surface of the steel element is in the range of 0.8 to 1.3 wt % and nitrogen concentration on the surface of the steel element is 0.2 to 0.8 wt %.
Further, in the present invention, a rolling bearing comprises an inner race, an outer race and a plural rolling elements. At least one of the inner race, the outer face and the rolling elements comprises a steel element containing: 0.2 to 1.2 wt % of C; 0.7 to 1.5 wt % of Si; 0.5 to 1.5 wt % of Mo; 0.5 to 2.0 wt % of Cr; 0.1 to 0.3 wt % of Ti and 12 ppm or less of O. The steel element is solution heat-treated, and thereafter, at least one of the inner race, the outer race and the rolling elements is quenched and tempered so that TiC having a size of 0.1 xcexcm or less is precipitated on a surface of said steel element.